|Publication number||US5046840 A|
|Application number||US 07/286,334|
|Publication date||Sep 10, 1991|
|Filing date||Dec 19, 1988|
|Priority date||Dec 19, 1988|
|Also published as||EP0374607A1|
|Publication number||07286334, 286334, US 5046840 A, US 5046840A, US-A-5046840, US5046840 A, US5046840A|
|Inventors||John B. Abbiss, Anthony E. Smart, Roger P. Woodward|
|Original Assignee||The Titan Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (8), Referenced by (14), Classifications (20), Legal Events (13)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This invention relates to improvements in a system for determining atmospheric data relating to the movements of an airborne vehicle. More particularly, the invention relates to improvements in a system included in the airborne vehicle for using energy scattered from aerosol particles in the atmosphere to determine a function of the movement and attitude of the airborne vehicle in the atmosphere. The invention further relates to a system for use with a laser to regulate the operating temperature of the laser.
Mechanical instruments have long been used to measure the relative speed between a moving object such as an airborne vehicle and the free airstream through which the airborne vehicle is moving. These mechanical instruments determine the kinetic pressure exerted by the moving airstream on a first defined area disposed on the airborne vehicle and facing the airstream. The mechanical instruments also determine the static pressure exerted on a second defined area disposed on the airborne vehicle in a substantially perpendicular relationship to the first defined area. The systems then compare the kinetic and static pressures to determine the relative air speed of the vehicle.
The mechanical instruments now in use typically employ Pitot tubes, pneumatic tubing and pressure transducers which are exposed to the external environment and are accordingly subject to degraded performance resulting from calibration changes from various causes such as aging or changes in temperature. They are also subject to catastrophic failures as a result of accidental breakage. Furthermore, they protrude physically into the airflow and provide a drag on the movement of the airborne vehicle.
As air navigation becomes increasingly complex, it becomes important to determine other data than the movement of the airborne vehicle relative to the ground. For example, it becomes increasingly important to know the characteristics of the air flow around the vehicle at each instant so that the response of the vehicle to such air flow can be properly controlled. The equipment now in use and discussed in the previous paragraphs has not been found satisfactory to provide the sensitive and accurate data which is now often required.
A considerable effort has been made for a long period of time, and substantial sums of money have been expended during such period, to develop a system which will overcome the disadvantages discussed above. For example, systems have been developed using aerosol particles in the atmosphere to obtain desired air data. Such systems have directed energy from the airborne vehicle in such forms as substantially coherent light and/or radiation to the aerosol particles and have received coherent light scattered from the aerosol particles. Such systems have then processed the received signals to obtain the desired data. Although such systems appear to be promising, they have not yet demonstrated the performance that may be realized by this invention and do not provide as accurate, sensitive and reliable information as may otherwise be desired.
In co-pending application Ser. No. 080,334, now U.S. Pat. No. 4,887,213 filed by Anthony E. Smart and Roger P. Woodward on July 31, 1987, for "Systems for, and Methods of, Providing for a Determination of the Movements of an Airborne Vehicle" and assigned of record to the assignee of record of this application, a system is disclosed and claimed for overcoming the above disadvantages. In one embodiment, light directed from a moving airborne vehicle and scattered from particles in the atmosphere produces, at first and second detectors at the vehicle, signals indicative of such scattered light. To reduce the effects of noise from stray light, the optical signals are spatially and spectrally filtered before detection. After optical detection, the electronic signals are further conditioned by amplification and special filtering.
The resultant signals are converted to digital signals. The digital signals are edited and accepted if they satisfy certain conditions pertaining to a selected threshold varied in accordance with the average amplitude level of the noise plus signal. The digital sampled signals from each particle are grouped. A centroid, based upon a weighting of the signals in each group in accordance with amplitude and time, is determined to represent the most probable time at which the particle crossed the peak of the illustrated region.
The peak amplitude of each signal from the first detector is paired with the peak amplitude of the successive signals from the second detector. The time difference between the paired signals, and their product amplitudes, are determined. The amplitude products are separated into successive bins on the basis of the time difference between the signals in each pair. The amplitude products in each bin are averaged. The bin with the greatest average amplitude product and the two (2) adjacent time bins are then selected.
The median time in the bin having the highest average product amplitude is used as a first approximation to the transit time of a particle between the two sheets. An estimate with enhanced accuracy may be obtained by calculating the "centroid", by a method analogous to that used above, of the distribution of events in the three (3) chosen bins. The bins may be of a width chosen to optimize the accuracy available from a small number of particle transits. Under certain circumstances, one event represented by the detection of the light reflected from a single particle is sufficient to obtain the required accuracy. The movement of the airborne vehicle may be determined from the selected time difference. Replication of the transit system to provide at least three pairs of illuminated regions may permit the direction to be obtained also.
This application discloses and claims improvements on the system disclosed and claimed in application Ser. No. 080,334. In one of these improvements, a plurality of lasers, each regulated to operate at a particular temperature, are supported by a manifold to direct coherent light into space. The regulation may be provided by producing pulses of a trickle current of a particular magnitude through the laser, measuring the voltage required to produce the trickle current and adjusting the characteristics of a thermoelectric member in accordance with the magnitude of such voltage to adjust the rate at which the thermoelectric member transfers heat from the laser.
The lasers produce substantially parallel and thin beams of light beams in pairs. The light beams in each pair provide an optimum angle for the interception by such paired beams of particles having individual trajectories in space. These particles scatter the light to a receiving lens system disposed within the manifold internally to the lasers. The received light then passes through masks which produce light beams in a spatial pattern corresponding to the pattern of the light beams from the lasers. The received light beams passing through the masks are detected to produce signals indicative of the light in such beams.
The manifold temperature may be regulated to maintain the optical characteristics of the lasers and the receiving system at an optimum value. The regulation may be provided by disposing heat sleeves on the manifold periphery, preferably in both axial and annular directions, and disposing in each heat sleeve a porous wick and a material convertible between liquid and gaseous forms. At positions above the regulated temperature, the liquid vaporizes and travels through the wick toward cooler spots where it vaporizes. It will be appreciated that the manifold temperature may be regulated by other means than that disclosed above.
In the drawings:
FIG. 1 is a schematic perspective view of an aircraft and of the disposition of the apparatus of the invention in the aircraft for directing light toward a particle in the atmosphere and for receiving fight reflected from the particle;
FIG. 2 is an elevational view of one embodiment of the apparatus constituting this invention;
FIG. 3 is a sectional view of the apparatus shown in FIG. 2 and is taken substantially on the line 3--3 of FIG. 2;
FIG. 4 is an enlarged schematic view of the relative disposition of different light beams produced by lasers in the apparatus shown in FIGS. 2 and 3;
FIG. 5 is an enlarged schematic view of the disposition of masks, and slits in the masks, in the apparatus shown in FIGS. 2 and 3 for operating on the light reflected by particles in the atmosphere;
FIG. 6 is a schematic view of heat pipes associated with the apparatus shown in FIG. 2 and 3 for regulating the temperature of the apparatus shown in FIGS. 2 and 3;
FIG. 7 is an enlarged fragmentary sectional view of one of the heat pipes shown in FIG. 6;
FIG. 8 is a schematic view of one of the lasers included in the apparatus shown in FIGS. 2 and 3 and of members associated with the laser for regulating the temperature of the laser;
FIG. 9 is an enlarged fragmentary schematic view of certain of the members shown in FIG. 8; and
FIG. 10 is a graph schematically illustrating the regulating action of the temperature regulator shown in FIGS. 8 and 9.
The apparatus constituting this invention is adapted to be used in a system such as disclosed and claimed in application Ser. No. 080,334 filed by Anthony E. Smart and Roger P. Woodward on July 31, 1987, for "System For, and Methods of, Providing for a Determination of the Movement of an Airborne Vehicle in the Atmosphere". Co-pending application Ser. No. 080,334 is assigned of record to the assignee of record of this application. Co-pending application Ser. No. 080,334 discloses the system of this invention in considerable detail. This application discloses and claims certain improvements in the system of co-pending application Ser. No. 080,334.
The apparatus constituting this invention may be disposed on an airborne vehicle 10 (FIG. 1) to direct substantially coherent light in thin beams toward particles, such as a particle 12, in space. The coherent light is scattered by the particles 12 back to the airborne vehicle 10. The scattered light is then processed at the airborne vehicle 10 to indicate the flight characteristics of the airborne vehicle with great accuracy.
In one embodiment of the invention, a manifold 16 (FIGS. 2 and 3) may be included in the apparatus constituting this invention and may be made from a suitable material such as a steel or a stainless steel or a composite material. A plurality of lasers generally indicated at 18 may be coupled to the manifold 16 around the external periphery of the manifold. The lasers 18 may be paired as at (a) 18a and 18 (b), 18c and 18d and (c) 18e and 18f. A manifold 20 (not shown) may be coupled to the manifold 16 and this manifold may be in turn coupled to a housing (not shown).
The lasers 18a-18f may be constructed in a conventional manner to produce substantially coherent light at a particular frequency and to direct such coherent light toward the particles 12 in space. As will ba seen, the lasers 18a-18f are disposed to direct the substantially coherent light on a slightly convergent basis. The lasers 18a and 18b produce thin beams of light having a spatial pattern respectively indicated at 26a and 26b in FIG. 4; the lasers 18c and 18d produce thin beams of light respectively indicated at 26c and 26d in FIG. 4; and the lasers 18e and 18f produce thin beams of light respectively indicated at 26e and 26f in FIG. 4.
The thin light beams 26a-26f may be disposed to travel into the plane of the paper in FIG. 4. As will be seen, the thin beams 26a and 26b, the thin beams 26c and 26d and the thin beams 26e and 26f are paired. The thin light beams in each pair are disposed relative to each other such that the particles 12 will have the widest trajectory angle in moving between the beams in such pair while intersecting the beams. This may be seen from a trajectory 28 between first diagonally opposite ends of the thin light beams 26a and 26b and a trajectory 30 at second diagonally opposite ends of such thin light beams.
As will be seen, in each of the trajectories 28 and 30 the particles 12 intersect the beams passing through the thin light beams 26a and 26b at the extremities of each beams. As a result, the trajectories 28 and 30 define the limits of the particle trajectories for intercepting the thin light beams 26a and 26b. The angles produced between a median trajectory 32 and each of the trajectories 28 and 30 are substantially equal.
The thin light beams 26a and 26b are displaced in a first direction (downwardly in FIG. 4) in the plane of the paper from the thin light beams slits 26c and 26d. Similarly, the thin light beams 26e and 26f are disposed between the thin light beams 26a and 26b and the thin light beams 26c and 26d. If the thin light beams 26e and 26f are considered to extend in a perpendicular direction in FIG. 4 in the plane of the paper, the thin light beams 26a and 26b and the thin light beams 26c and 26d form equal angles with the thin light beams 26e and 26f. However, the beams 26c and 26d slope in an opposite direction from the beams 26a and 26b. The beam 26d is displaced upwardly from the beam 26c to maximize the particle trajectories intersecting these beams as discussed in the previous paragraph. Similarly, the beam 26b is displaced downwardly from the beam.
Each of the lasers 18 may be provided with a pair of electrical terminals 40 and 42 (FIG. 8). The terminal 40 may be made from a suitable material such as gold and the terminal 42 may be made from a suitable material such as copper. A layer 44 may be disposed intermediate the terminals 40 and 44 and may be provided with a suitable thickness such as approximately two hundred microns (200 μm). The layer 44 may be made from a suitable material such as gallium arsenide. When a pulse of a positive voltage is applied to the terminal 40 from a variable voltage source 41 and a negative voltage is applied to the terminal 42 from the source, light having substantially coherent characteristics is emitted from the intermediate layer 44 at a particular frequency in a direction such as indicated at 46 in FIG. 5. It will be appreciated that this is a relatively simplified explanation since these features are well known in the art.
A heat sink 48 made from a suitable material such as copper is disposed in abutting relationship to the terminal 42 to transfer to the heat sink heat generated by the transmission of light by the intermediate layer 44. An electrical insulator 50 is disposed in abutting relationship with the heat sink 48 and a thermoelectric cooler 52 is in turn disposed in abutting relationship with the insulator 50. A suitable unit of the thermoelectric cooler 52 may be obtained from Marlow Inductries, Inc., of Dallas, Tex.
The thermoelectric cooler 52 includes a pair of semi-conductor members 54 and 56 (FIG. 9), the member 54 being an n-type semi-conductor and the member 56 being a p-type semi-conductor. The members 54 and 56 are connected by a bar 58 at the end adjacent to the insulator 50. Terminals 60 and 62 are respectively attached to the semi-conductor members 54 and 56 at the end opposite the insulator 50. A source 64 of electrical pulses is connected between the terminals 60 and 62. The source 64 is adapted to produce pulses having an adjustable rate and fixed duration under the control of the voltage from the source 64. Alternatively, the source 64 is adapted to produce pulses having a fixed rate and a variable duration under the control of the voltage from the source 64.
As previously described, each of the lasers 18 is constructed in a conventional manner to produce substantially coherent light at a particular frequency. This causes the laser 18 to generate heat. This heat is introduced to the heat sink 48 which dissipates some of the heat and introduces the remainder of the heat to the thermoelectric cooler, generally indicated at 52, for dissipation by the cooler.
The laser 18 is periodically turned off for a small period of time. When the laser 18 is turned off, a current source 66 (FIG. 8) is connected to the terminal 40 to produce a flow of a current of a low magnitude through the terminals 40 and 42 and the intermediate layer 44. For example, the current may have a suitable value such as approximately one milliampere (1 ma). The voltage required to produce this current varies in accordance with the temperature at the intermediate layer 44.
The interrelationship between the temperature of the laser at the intermediate layer 44 and the voltage required to produce the current of the particular value such as approximately one milliampere (1 mA) is illustrated in FIG. 10. This current is illustrated at IL in FIG. 10. In FIG. 10, the current through the intermediate layer 44 is illustrated along the vertical axis and the voltage for producing this current is shown along the horizontal axis. In FIG. 10, the relationship between current and voltage for a temperature T1 is illustrated at 70 and the relationship between current and voltage for a temperature T0 is illustrated at 72 in FIG. 5.
For an "ideal" diode, the relationship between voltage, current and temperature is given by the equation
IL =IO e qV /kT (1)
In the above equation,
IO =a constant since it constitutes a predetermined current such as one milliampere (1 ma);
q=a constant; and
IO =a constant for any given laser.
Equation (1) can be rewritten as ##EQU1## This can be further rewritten as ##EQU2## As will be seen, the temperature of the laser is related to the voltage required to produce the current of one milliampere (1 mA) through the laser.
The measured temperature obtained from the voltage required to produce the pulse current of one milliampere (1 mA) is introduced to the source 64 to control the rate at which pulses are produced by the source. These pulses are introduced to the thermoelectric cooler 52 to obtain the flow of current through the semi-conductor members 54 and 56. This flow of current causes the junction of the thermoelectric cooler 52 adjacent the insulator 50 to have a higher temperature then the junction of the thermoelectric cooler adjacent to the terminals 60 and 62. Heat accordingly flows through the thermoelectric cooler 52 in a direction away from the heat sink 48.
As will be appreciated, the difference in temperature between the two junctions in the thermoelectric cooler 52 is dependent upon the rate at which the pulses are introduced by the source 64 to the thermoelectric cooler. For example, as the temperature at the intermediate layer 44 increases, the rate of introduction of pulses from the source 64 to the thermoelectric cooler 52 increases. This causes the thermoelectric cooler 52 to transfer an increased amount of heat from the heat sink 48. In this way, the controlled operation of the thermoelectric cooler 52 causes the temperature at the intermediate layer 44 of the laser 18 to be regulated.
The substantially coherent light from the lasers 18 is reflected by the particles 12 back to the manifold 16. The reflected light is received by a lens 80 (FIG. 3) within the manifold 16. The received light is collimated by lenses 82 and is partially focused on a mirror 84. The light is then reflected by the mirror 84 to a lens 86. A mask 88 is disposed on the surface of the lens and is provided with a plurality of slits 90 (FIG. 5) in a pattern corresponding to the pattern of the light beams from the lasers 18. This pattern is shown in FIG. 4 and has been described fully above. The light is then collimated and focused as by lenses 92 (FIG. 3) on a detector 94. The detector 94 produces signals in accordance with the light pulses passing through the slits 90. The signals are then processed in a manner such as disclosed in detail in co-pending application Ser. No. 080,334.
The temperature of the manifold 16 may be regulated to control the optical characteristics of the light transmitted by the lasers 18 and the optical characteristics of the receiving lenses including the lens 80, the lenses 82, the mirror 84, the lens 86 and the lenses 92. In this way, the apparatus constituting this invention can provide accurate determinations of the function of the movement and attitude of the airborne vehicle in the atmosphere.
To regulate the temperature of the manifold 16, heat pipes generally indicated at 100 (FIGS. 6 and 7) may be disposed around the periphery of the manifold. Some of the heat pipes 100 may be disposed in an annular direction as indicated at 100a in FIG. 6 and other heat pipes may be disposed in an axial direction. It will be appreciated that still other heat pipes may be disposed in a direction having both annular and axial components.
Each of the heat pipes 100 includes a hollow sleeve 102 (FIG. 7) made from a suitable material such as steel or stainless steel. A wick 104 made from a suitable porous material such as steel is disposed within the sleeve 102 adjacent the inner periphery of the sleeve. A material 106 such as methylene chloride or sodium is disposed within the sleeve 102. The material 106 such as methylene chloride or sodium is convertible between the liquid and gaseous states at a temperature relatively close to the temperature at which the manifold 16 is to be regulated.
When the temperature of the manifold 16 increases above the regulated value at a particular position, the material 106 at this position vaporizes. In vaporizing, the material 106 absorbs heat. The vaporized material 106 then travels through the wick 104 to a position at which the temperature is less than the regulated value. At this position, the material condenses to a liquid and gives up heat. This causes the temperature at this position to rise toward the regulated value. In this way, the temperature of the manifold 16 at the different positions is regulated at a particular value.
The apparatus constituting this invention has certain important advantages. It provides a manifold which supports both the light-transmitting and light-receiving components and it regulates the temperature of the manifold to maintain the optical characteristics of the light transmissions and the light receptions at an optimum value. The apparatus of this invention also provides for the transmission and reception of beams of light having an optimum disposition relative to one another to provide for the interception of particles through optimum angles of movement relative to such beams.
The apparatus of this invention also provides for a precise regulation of the temperatures of the lasers to maintain the optical characteristics of the lasers within precise limits. It will be appreciated that the system for regulating the temperatures of the lasers may be used in other environments than in a system for determining a function of the movement and attitude of the airborne vehicle 10 in the atmosphere.
Although this invention has been disclosed and illustrated with reference to particular embodiments, the principles involved are susceptible for use in numerous other embodiments which will be apparent to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.
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|U.S. Classification||356/28, 359/503, 257/930, 372/35, 257/715, 372/36|
|International Classification||G01P5/18, H01S5/024, G01P1/00, G01P5/26|
|Cooperative Classification||Y10S257/93, G01P1/006, G01P5/26, H01S5/06804, H01S5/02415, G01P5/18|
|European Classification||H01S5/024A2, G01P5/18, G01P1/00C, G01P5/26|
|Dec 19, 1988||AS||Assignment|
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